As well known, most of portable information devices such as portable terminals (mobile phone, smart phone, smart device, navigation, watch phone, wearable device and the like) and the like generally have a touch type small-sized keypad (touch panel). Although the small-sized keypad has been conventionally used for short message service (SMS), it is recently widely used for memo, various data processing using the portable information devices, and the like.
Recently, the small-sized terminal such as a wearable device, e.g., a smart watch or the like, is spreading rapidly. In general, the small-sized terminal has a subminiature touch panel that is relatively smaller than that of a portable terminal due to the size of the entire product.
In that case, the subminiature touch panel attached to the small-sized terminal provides a relatively small input space, which makes it difficult to input characters by using a conventional keyboard input technique using a qwerty keyboard or the like.
In addition, in the conventional small-sized terminal, a large number of character buttons need to be arranged in a relatively small input space and, thus, a size of each character button becomes relatively smaller. Accordingly, a typing error is made frequently. When the typing error is made, it is required to delete a mistyped character and input a desired character. As a result, the character input speed becomes considerably slower.
Reference Document: Korean Patent No. 10-1568716